During the 1980s, Saddam Hussein’s Iraqi regime used some of these deadly agents in its war with Iran and against its own Kurdish civilians. While it is uncertain that Iraq could launch such attacks today, other nations — including Iran, Syria, North Korea, Russia, and China — are believed to possess large stockpiles of chemical and biological weapons.

Now the question is: Would the United States withstand a large-scale assault with such deadly agents?

If the anthrax attacks of 2001 are any gauge, the answer isn’t encouraging. With only 22 infections, that incident was, compared to what could have happened, a very minor outbreak. Yet our public health system was pushed to the brink. If those precision-manufactured spores had been spread, not through the mail (a clumsy means of delivery), but through the ventilation system of a building, thousands could have succumbed.

An even more horrific scenario involves smallpox, which is a contagious disease; if, say, terrorists had secretly released that deadly virus through simple aerosol devices at a dozen football stadiums on a Saturday afternoon, public health authorities would be racing to catch up days later. In that time, a geometrically growing outbreak would paralyze the nation, conceivably killing tens of thousands before being brought under control.

Chemical and biological weapons each present their own unique public health challenges. Most chemical agents — whether they produce their misery by blistering, choking, disabling nerve pathways, or interfering with the absorption of oxygen in the bloodstream — work swiftly. Death can come within minutes.

Anthrax — what did we learn? Public reaction to the scattered but nerve-wracking cases of anthrax may be a pale presentiment of the country’s response to a more widespread and murderous terrorist attack.

The first rescuers on the scene of an attack would be police, firefighters, and paramedics — perhaps working in concert as part of the Metropolitan Medical Response System (MMRS). Coordinated by the federal Office of Emergency Preparedness (part of the Department of Health and Human Services), MMRS began in 1996 with funding from the Defense Against Weapons of Mass Destruction Act. (MMRS training began in Washington, D.C., and moved on to Atlanta in 1997. Since then, the program has trained dozens of localities and will eventually extend nationwide.) After the MMRS teams deployed, area hospitals would quickly fill with bona fide casualties needing triage and elaborate decontamination. Adding to the caseload, and to the crowds, would be the “worried well,” who always flock to hospitals during national emergencies.

Biological terrorism would bring a more insidious mayhem, because the disease would silently incubate for days or weeks before symptoms became apparent. The first victims might drift into emergency rooms, doctors’ offices, and urgent care clinics. They would have vague flu-like symptoms, since most infectious diseases begin with aches, fever, and chills — the immune system’s early response to infectious invaders. At this stage of the outbreak, clues may be too subtle and too diffuse to pick up. If this early wave of patients could walk out, they would probably be sent home with a diagnosis of flu — as, tragically, was a Washington, D.C. postal worker in October 2001, who hours later died of inhalation anthrax. If the disease were contagious, the infection would spread.

In both of these scenarios, only a robust public health system — one that instantly registers aberrant syndromes and anomalies in disease rates, figures out the problem, and quickly intervenes — could curb the spread and devastation of disease. Though New York City and other localities have implemented the early stages of such a surveillance system, the full-blown plan would surpass any public health system anywhere in the world. In this visionary model, doctors and nurses would immediately recognize the unfamiliar symptoms of a wide spectrum of chemical and biological agents. State and local health departments would continually collect data from hospitals about patients with suspicious pneumonias, meningitis, blood infections, diarrhea, botulism-like symptoms, rashes with fever, and fatal unexplained fevers (symptoms that, en masse, suggest deliberate infection). Pharmacies would report spikes in over-the-counter drug sales. Laboratories would perform rapid tests that would unmask an intentionally released pathogen. Extra hospital beds and emergency supplies would be in place. A wide range of vaccines and antibiotics and antitoxins would be stockpiled. And officials would know in advance precisely the decisions — about vaccinations, quarantines, travel restrictions, and so on — that they would make in a crisis.

Such a system pays double on its investment. While girding for the dangers of bio-terrorism, we also prepare for more common contingencies — from schoolyard meningitis or salad bar hepatitis to the next deadly flu pandemic or outbreak of drug-resistant tuberculosis.

Unfortunately, this ideal is a long way off. Thirty percent of all U.S. hospitals are in the red and nearly 60 percent of academic medical centers can’t meet their operating expenses. As a result, there’s no slack in the system — no “surge capacity,” to use public health jargon — should hundreds or thousands of people in a city or town suddenly get sick. Hospitals run out of beds during an unremarkable flu season. This past April, the American Hospital Association reported that one in three emergency rooms are currently so crowded they must send away incoming ambulances — and that’s on an average day, with no catastrophe to contend with. In a 2000 survey of 30 U.S. hospitals, published by the ANNALS OF EMERGENCY MEDICINE in November 2001, none were prepared to handle large numbers of casualties caused by biological, chemical, or nuclear weapons; indeed, 26 facilities reported that they could only handle 10 to 15 victims at once. Since the 9/11 terrorist attacks, the federal government has siphoned hundreds of millions of dollars to state and local health departments to gird for terrorism, and in many cities and towns hospitals have drawn up plans to share the workload should a massive assault take place.

The practicalities of care taking aren’t the only worry. If the United States suffered a chemical or biological attack, public health officials would need to communicate clearly and openly with American citizens. Public reaction to the scattered but nerve-wracking cases of anthrax — with drug stores running out of the antibiotic Cipro and gas masks selling like hotcakes on the Internet — may be a pale presentiment of the country’s response to a more widespread and murderous terrorist attack. If we learned anything last fall, it’s that in the fog of war, fear itself can spread like a contagion.

Madeline Drexler is a Boston-based science and medical journalist and the author of “Secret Agents: The Menace of Emerging Infections.” A former medical columnist for THE BOSTON GLOBE MAGAZINE and an MIT Knight Science Journalism Fellow, Drexler’s work has appeared in THE NEW YORK TIMES, THE AMERICAN PROSPECT, and other national publications.